1. Field of the Invention
The present invention relates to a front end module capable of significantly reducing a leakage voltage that may be generated in a signal transmission mode while constituting a parallel switch circuit having a relatively reduced number of switch devices, and thus preventing a deterioration of linearity and breakage of elements, by disposing a parallel switch circuit between a node included in a matching circuit unit and a ground node.
2. Description of the Related Art
A front end module (FEM) is a module of a mobile device or the like, in which high-frequency components, such as a SAW filter, a diplexer, a low pass filter, an RF switch, and the like, are integrated into a single module to significantly reduce an area occupied thereby, and is a necessary component in an electronic device having a communications function. In particular, a front end module employed in a mobile device may serve as a filter for separating a transmission signal and a reception signal to prevent signal collision and selectively pass only signals having a particular frequency.
Generally, a single chip front end module applied to the mobile device includes an amplification circuit unit amplifying a signal, a switch circuit unit transmitting an output signal of the amplification circuit unit to an antenna, and the like. The switch circuit unit is controlled to be turned on or off depending on the operation mode (a signal transmission mode or a signal reception mode) of the front end module, and a serial switch circuit unit and a parallel switch circuit unit may be disposed between an output terminal of the amplification circuit unit and the antenna and between the output terminal of the amplification circuit unit and a ground terminal, respectively.
When the switch circuit unit is turned on, a voltage is barely applied to switch devices constituting the switch circuit unit, and thus linearity of the switch devices barely influences an operation of the entire circuit of the front end module. On the contrary, when the switch circuit unit is turned off, a predetermined voltage is applied to the respective switch devices. Since the voltage at which one switch device may withstand is fixed, the switch circuit unit is required to be configured in a stack structure in which several switch devices are connected, in order to improve stability of the entire circuit. As such, when the amount of switch devices included in the switch circuit unit is increased, linearity characteristics and withstand voltage may be improved, but the size of the module may be increased and the price thereof may be increased.
In the Related Art Documents below, Patent Document 1 is directed to a multiband matching circuit and an amplification circuit, and discloses a multiband amplification circuit including an amplification circuit and a matching circuit, and Patent Document 2 is directed to a high-efficiency multimode power amplification device, and discloses an amplification circuit including an impedance matching circuit and an amplification circuit. However, Patent Documents 1 and 2 fail to disclose a method for decreasing the amount of switch devices included in a switch circuit unit by changing the configuration in which an output terminal of the amplification circuit is connected with the switch circuit unit.